Embed Size (px)
Citation preview
www.elsevier.com/locate/ssi
Solid State Ionics 176
Structure–intercalation relationships in LiNiyCo1-yO2
T. GrossT, Th. Buhrmester, K.G. Bramnik, N.N. Bramnik, K. Nikolowski,
C. Baehtz, H. Ehrenberg, H. Fuess
Institute for Materials Science, Darmstadt University of Technology Petersenstr. 23, D-64287 Darmstadt, Germany
Received 19 August 2004; received in revised form 8 February 2005; accepted 8 February 2005
Abstract
The influence of the annealing temperature on the degree of cation-disordering in the layered structures was examined for three different
compositions of LiNiyCo1-yO2 ( y =0.2, 0.66 and 0.75, respectively). A minimum in cation-disorder is found for annealing temperatures
between 700 and 800 8C for y =0.75, between 750 and 810 8C for y =0.66 and a less pronounced minimum between 795 and 870 8C for
y =0.2. One optimum annealed sample with y =0.75 was used for an in situ characterisation using synchrotron radiation. The obtained
structural data correlate well with the electrochemical data. The known phase transition occurring during the first cycle was closely observed
by ADXRD (angular dispersive X-ray diffraction). The two states of the material during the first cycle could be distinguished and the
obtained data were processed by Rietveld refinement.
D 2005 Elsevier B.V. All rights reserved.
Keywords: LiCoO2; LiNiO2; Li-ion battery; In-situ characterisation
1. Introduction
The structures of both end members of the solid
solution LiNiyCo1-yO2 (LiNiO2 for y=1 and LiCoO2 for
y =0, respectively) are known since the middle of the last
century [1,2]. The two compounds are isostructural
(spacegroup R3̄m) with only small differences in lattice
parameters. The physical properties and electrochemical
behaviour of the mixed system, i.e. LiNiyCo1-yO2 [3–11]
are well known. These materials are used as positive
electrode in secondary Li-ion batteries. In commercially
used systems1 this material is used as cathode and forms
together with graphite anode materials so-called brocking-chairQ batteries. A major advantage of the Ni/Co-mixed
system over the end members of the system is an easier
synthesis compared to LiNiO2 on one hand (which has to
our knowledge not yet been synthesised strictly stoichio-
0167-2738/$ - see front matter D 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ssi.2005.02.008
T Corresponding author. Tel.: +49 6151 16 6359; fax: +49 6151 16 6023.
E-mail address: [email protected] (T. Gross).1 At present most cellular phones and laptop-computers are using Li-ion
batteries of this type.
metrical) [12–16]. On the other hand Ni is cheaper than Co
and less harmful to the environment.
Liu et al. reported on the influence of annealing time and
temperature on the degree of cation disorder, i.e. the amount
of Ni/Co in the Li-layers and vice versa, and electrochemical
behaviour for LiNi0.8Co0.2O2 [11]. They calculated the
degree of cation-disorder by constraining the parameters
for the occupation of Li- and Ni/Co-sites, respectively. In
their work it was shown that, by using the sol-gel technique,
the annealing temperature as well as the annealing time could
be lowered (in contrast to direct solid-state reaction or co-
precipitation methods). Accordingly, they found a minimum
in the degree of cation disorder (as well as the cell parameter
a) with respect to the annealing time and temperature. The
effect of annealing temperature on cation disorder for
different Ni/Co ratios ( y =0.75, 0.66, 0.2) is reported here.
Furthermore, the structural changes during reversible dein-
tercalation and intercalation of Li has been investigated by in
situ synchrotron diffraction. Ex-situ data cannot provide
reliable information, because of the sensitivity of the
electrodes and electrolyte to air and humidity. Structural
changes due to relaxation phenomena can also be misleading
in ex-situ studies.
(2005) 1193–1199
Aluminium
Stainless Steel
TeflonTrovidur
Kapton Foil
Lithium Foil
Cathode
Spring
Beam
O-Rings
Separator
Fig. 1. Schematic drawing of the in-situ cell (cross section).
Table 2
Structure parameters for composition P II
Temperature
[8C]a [2] c [2] c/a ratio Cation-
disordering
[%]
600 2.8735(7) 14.2158(79) 4.9472(6) 10.1(31)
650 2.8628(3) 14.1516(29) 4.9433(4) 5.9(13)
700 2.8597(1) 14.1422(10) 4.9454(3) 2.8(5)
750 2.8583(1) 14.1554(4) 4.9524(2) 1.5(2)
765 2.8589(1) 14.1581(4) 4.9523(2) 1.1(2)
780 2.8589(1) 14.1578(4) 4.9522(2) 1.5(2)
795 2.8562(1) 14.1462(4) 4.9529(2) 1.6(2)
810 2.8589(1) 14.1592(4) 4.9526(2) 1.9(2)
825 2.8591(1) 14.1609(4) 4.9530(2) 2.8(2)
840 2.8613(1) 14.1687(3) 4.9519(2) 4.7(2)
855 2.8595(1) 14.1601(4) 4.9520(2) 3.8(2)
870 2.8633(1) 14.1778(3) 4.9515(2) 4.4(2)
885 2.8624(1) 14.1726(4) 4.9512(2) 5.3(2)
900 2.8649(1) 14.1818(4) 4.9502(2) 9.9(2)
T. Gross et al. / Solid State Ionics 176 (2005) 1193–11991194
Here we present a more detailed examination of the
influence of synthesis conditions on the structure and
electrochemical behaviour combined with in-situ XRD
using synchrotron radiation.
2. Experimental
2.1. Sample preparation
The raw cathode materials were synthesised using the sol-
gel technique. Precursors for all reactions referred to in this
paper were LiNO3 (Aldrich, 99.99%), Co(NO3)2d 6 H2O
(Aldrich, 99.999%) and Ni(NO3)2d 6 H2O (Alfa Aesar,
Puratronic, 99.9985%). Citric acid was added as complexing
agent in these reactions. The obtained precursors were pre-
calcined at 450 8C for 6 h (with a heating ramp of
approximately 100 8C/h). The so obtained material was
divided into several portions to investigate the influence of
the annealing temperature on the cation disorder. Final
calcination was performed at different temperatures (600–
900 8C) to examine the influence of the annealing temper-
ature on the structure and cation distribution of the material.
Table 1
Structure parameters for composition P I. The estimated standard deviations
(in brackets) are calculated in agreement with [23,24]
Temperature
[8C]a [2] c [2] c/a ratio Cation-
disordering
[%]
600 2.8784(5) 14.2052(59) 4.9350(18) 14.4(7)
650 2.8702(2) 14.1725(20) 4.9377(7) 7.2(4)
700 2.8652(1) 14.1624(6) 4.9428(3) 2.8(3)
750 2.8633(1) 14.1618(9) 4.9460(3) 2.1(3)
765 2.8638(1) 14.1673(5) 4.9470(2) 2.4(3)
780 2.8460(1) 14.0779(4) 4.9466(2) 2.3(3)
795 2.8455(1) 14.0780(4) 4.9476(2) 2.2(3)
810 2.8468(1) 14.0833(4) 4.9470(2) 4.2(3)
825 2.8478(1) 14.0887(5) 4.9473(2) 4.6(3)
840 2.8680(1) 14.1844(4) 4.9459(2) 5.1(2)
855 2.8708(1) 14.1931(4) 4.9440(2) 7.9(3)
870 2.8712(1) 14.1932(5) 4.9432(2) 9.0(3)
885 2.8737(1) 14.2033(4) 4.9425(2) 11.1(3)
900 2.8764(1) 14.2122(5) 4.9410(2) 13.6(3)
The sample compositions and annealing temperatures are
resumed in the following list: 600 8C, 650 8C, 700 8C, 7508C, 765 8C, 780 8C, 795 8C, 810 8C, 825 8C, 840 8C, 855 8C,870 8C, 885 8C, 900 8C.
Three different compositions were synthesised in this
way: LiNi0.75Co0.25O2 (samples are marked as P I),
LiNi0.66Co0.34O2 (P II) and LiNi0.2Co0.8O2 (P III). After
equivalent annealing periods of 10 h for all samples, heating
was switched off and the temperature dropped accordingly
at a rate of c100 8C/h.
2.2. Structural investigation
The obtained samples were precharacterised by X-ray
powder diffraction (XRD) using a Stadi-P diffractometer
(STOE) in transmission geometry equipped with a molyb-
denum X-ray tube (Mo–Ka1=0.709262), a curved Ge-
(111)-monochromator and a linear position sensitive detec-
tor (PSD) with an aperture of 68. The patterns were collectedin an angular range of 7–508 (2h) with a step width of 0.028
Table 3
Structure parameters for composition P III
Temperature
[8C]a [2] c [2] c/a ratio Cation-
disordering
[%]
600 2.8303(3) 14.0678(29) 4.9705(4) 2.1(12)
650 2.8306(3) 14.0651(27) 4.9690(4) 3.0(13)
700 2.8307(2) 14.0667(21) 4.9693(4) 2.2(10)
750 2.8294(1) 14.0891(6) 4.9795(3) 0.8(3)
765 2.8302(1) 14.0961(5) 4.9806(3) 0.7(2)
780 2.8301(1) 14.0954(4) 4.9805(2) 0.5(2)
795 2.8283(1) 14.0864(6) 4.9805(3) 0.4(2)
810 2.8296(1) 14.0934(4) 4.9808(2) 0.3(2)
825 2.8313(1) 14.1018(4) 4.9807(2) 0.6(2)
840 2.8296(1) 14.0936(4) 4.9807(3) 0.4(2)
855 2.8280(1) 14.0871(4) 4.9812(3) 0.8(2)
870 2.8305(1) 14.0974(3) 4.9806(2) 0.7(2)
885 2.8320(1) 14.1065(3) 4.9811(2) 0.7(2)
900 2.8314(1) 14.1036(3) 4.9812(2) 1.1(2)
Fig. 2. c/a ratios of different compositions: squares represent the data for
composition LiNi0.75Co0.25O2 (P I), filled circles the data for composition
LiNi0.66Co0.34O2 (P II) and triangles for LiNi0.2Co0.8O2 (P III).
Fig. 4. Charge–discharge curve of LiNi0.75Co0.25O2 (P I) annealed at 795
8C (sample CM2).
T. Gross et al. / Solid State Ionics 176 (2005) 1193–1199 1195
(2h). Rietveld refinement has been applied for data analysis
using WINPLOTR [17].
2.3. Electrochemical examinations
The binder used for pressing pellets was poly(vinylidene-
flouride cohexaflouropropylene) (PVF, Fluka). Carbon was
added (Acetylene carbon black, Strem chemicals, 99.99%) to
improve the electronic conductivity of the cathode powder.
The weight ratio active cathode material:binder:graphite was
85:10:5. The cathode mixture was prepared by grinding the
powders in an agate mortar. The pellets are hygroscopic, so
they were vacuum-dried (approximately 10-3 mbar) for 4 h at
c100 8C before usage in the electrochemical cell. The dried
pellets were put into the SWAGELOK-construction, using a
round piece of glass fibre filter as separator. A few drops of
electrolyte were added until the separator got soaked with
electrolyte (1M LiPF6 in a 1:1 mixture of dimethylcarbonate
Fig. 3. Degree of cation-disordering of different compositions: squares
represent the data for composition LiNi0.75Co0.25O2 (P I), filled circles the
data for composition LiNi0.66Co0.34O2 (P II) and triangles for LiNi0.2-Co0.8O2 (P III).
and ethylencarbonate). Metallic lithium from a lithium rod
was cut into thin slices (1–2 mm) and used as anode. During
mounting of the cell slight pressure was exerted on the
current collectors. A multichannel-potentiostat (VMP2/Z;
Ametek) was used in galvanostatic mode with potential
limitation to carry out the electrochemical examinations.
Potential limitations were set to 4.2 V and 1.9 V (measured
relatively to the redox system Li/Li+) with a constant current
of 0.1 mA. The other preset criterion for the reversal of
polarity was when the value of x reached the value 0.5 or 1 as
calculated from charge transfer by integration of the passed
current over time.
2.4. The in-situ cell
A method to examine the structure of the cathode
material could be to disassemble a cycled battery in a
glovebox and wash out the electrolyte of the cathode
0.6 0.7 0.8 0.9 1.01.5
2.0
2.5
3.0
3.5
4.0
4.5
Ew
e [V
]
x in LixNi
0,75Co
0,25O
2
Fig. 5. Charge–discharge curve of LiNi0.75Co0.25O2 (P I) annealed at 900
8C (sample CM1).
7 12 17 22 27 32 37 42 47 52 57 -28000
-18000
-8000
2000
12000
22000
32000
42000
52000
62000
72000
Inte
nsity
(a.
u.)
2 Theta
excluded region
(003)
(110) Li
(104) +(200) Al
(015)(113)
Fig. 6. Full pattern of LiNi0.75Co0.25O2 annealed at 810 8C; the phases are from top to bottom: LiNi0.75Co0.25O2 (state A), LiNi0.75Co0.25O2 (state B), metallic
lithium (anode), aluminium (current collector), unidentified phase (coming from the design of the cell, the corresponding reflections are absent, if not measured
in the in-situ cell).
T. Gross et al. / Solid State Ionics 176 (2005) 1193–11991196
material and put it in a sealed capillary for XRD measure-
ment. The disadvantage of this method is evident, because
usually one can expect relaxation processes after deinterca-
lation/intercalation. Furthermore one cannot see possible
structural changes during usage. Therefore the battery group
from the Institute for Materials Science, Darmstadt Uni-
versity of Technology, has built a device for in-situ X-ray
characterisation of battery materials (see Fig. 1)[18]. It was
designed for usage at high-intensity (and high resolution) X-
ray sources (synchrotron radiation) in transmission geom-
etry. The body of the cell is made of Trovidur (polymer;
registered trademark) using stainless steel and aluminium as
current collectors. The Al plunger has to be very thin in
Fig. 7. Cell parameter a for LiNi0.75Co0.25O2 (both states).
order to diminish absorption, but has to be mechanically
stable enough to maintain pressure on the electrodes
throughout the experiment. The sealing system consists of
several teflon parts, two O-rings and a Kapton foil on the
bopenQ end of the device. Data were collected at beamline
B2 of the DESY (Deutsches Elektronensynchrotron, Ham-
burg). The selected wavelength was 0.70987(1)2.
3. Results
3.1. Structural investigation
The structural model for Rietveld refinement is based on
the following atomic positions (these are the atomic
positions for LiNiO2, space group R3̄m, according to [1]):
Atom Atomic position Wyckoff site
Li (0,0,1/2) 3b
Ni (0,0,0) 3a
O (0,0,z)a 6c
a With zc0.25.
Ni and Co are treated as identical scatterers in this model,
but Ni/Co are permitted to occupy Li-sites and vice versa.
This cationic disorder, constrained to fixed overall compo-
sition and fully occupied sites, is a breal structureQparameter for the characterisation of the material.
The cell parameters obtained by Rietveld refinement are
given in Tables 1–3 and illustrated in Figs. 2 and 3,
Fig. 8. Cell parameter c for LiNi0.75Co0.25O2 (both states). Fig. 10. Cell volume for LiNi0.75Co0.25O2 (both states).
Profile fitting: cycle # 6
T. Gross et al. / Solid State Ionics 176 (2005) 1193–1199 1197
respectively. From these data it is obvious that an optimum
temperature range for a highly ordered material exists. For
composition P I this temperature region reaches from 700–
800 8C (see Fig. 3) with a minimum disorder at approx-
imately 795 8C. At lower temperatures (b650 8C) the
material is amorphous and at higher temperatures (N900 8C)the vapour pressure for Li presumably becomes so high that
considerable amounts of Li separate from the material,
resulting in a less ordered state.
The other two compositions (P II and P III) show a
similar behaviour, but with minimal disorder at different
temperature ranges. For composition P II (with y =0.66) the
optimum annealing temperature range reaches from 750 to
810 8C, with a minimum disorder around 765 8C. The
temperature range for P III ( y =0.2) is 795 to 870 8C, theminimum disorder occurs at approximately 810 8C.
3.2. Electrochemical examinations
The electrochemical performances of the different
compositions show clearly that more ordered samples work
Fig. 9. Phase fraction for LiNi0.75Co0.25O2 (both states).
much better (i.e. the cell polarization is lower for the more
ordered material and the irreversible loss of capacity is also
lower, see Fig. 3 and Table 1). Two charge–discharge curves
are shown as representatives to elucidate the differences in
their electrochemical behaviour, correlated with the degree
of cation-disordering (see Figs. 4 and 5). For both cathode
mixes the same active material (P I, LiNi0.75Co0.25O2) and
the identical ratio for mixing have been used. The difference
is the annealing temperature (900 8C for sample CM1 and
795 8C for sample CM2). The irreversible loss of capacity is
lower for sample CM2. The cell built with sample CM1
does not work properly at all; it loses almost half of its
capacity in the first cycle. Also a very high polarization
(approximately 0.5 V) is observed.
3.3. The in-situ study
The cathode material used in this experiment was
LiNi0.75Co0.25O2 annealed at 810 8C. The in-situ cell was
2700
210029.3 29.2 29.5 29.6 29.7 29.8 29.9 30.0 30.1 30.2 30.3 30.4
3300
3900
4500
5100
5700
6300
6900
7500
Inte
nsity
(a.
u.)
Fig. 11. Dual peak fit of the (113)-reflection (most pronounced splitting) to
demonstrate the significance of the usage of a two-phase structural model
(the 23rd diffractogram is illustrated here).
6000
4000
200029.49 29.57 29.65 29.73 29.81 29.89 29.97 30.05 30.13 30.21 30.29
8000
10000
12000
14000
Inte
nsity
(a.
u.)
Fig. 12. Comparison of the (113)-reflection from the first and the 23rd diffractogram.
T. Gross et al. / Solid State Ionics 176 (2005) 1193–11991198
connected to the VMP and cycled with I =8.4 mA/g. The
reversal of polarity criterion was the value of x in
LixNi0.75Co0.25O2, either 0.5 or 1 depending on deinterca-
lation or intercalation mode. Approximately every 15 min a
diffractogram was measured2. One complete cycle was
measured in this way. One full pattern is depicted in Fig. 6
as an example. The excluded region has been introduced,
because a little hump appears in this 2h-region, probablydue to the added partly crystallized carbon. The broadening
and characteristic splitting scheme of reflections indicate the
coexistence of two isostructural states with only slightly
different cell parameters (at the beginning of the experi-
ment). The data obtained via Rietveld refinement are
illustrated in Figs. 7–11.
In the beginning of the experiments both states3 of the
cathode material did not show significant differences in
lattice parameters. Therefore the first 15 diffractograms
measured were analysed using a one-phase structural
model. When the progressive splitting of reflections had
gone so far, that the two corresponding reflections could
be clearly distinguished, a two-phase structural model for
Rietveld-refinement was used, because it is able to explain
the drastic changes in the two states during cycling. The
diffractograms measured at the beginning of deintercala-
tion exhibit sharp reflections (i.e. the full width at half
maximum is narrow; see Fig. 12), showing the good
crystallinity of the material. Certain reflections show
broadening, as the value of x is continuously lowered4.
At a value of approximately x =0.9, it becomes obvious
that the observed broadening of reflections is a splitting of
two reflections belonging to two states, whereby the lattice
2 The total number of measured diffractograms is 160 for the complete
charge–discharge cycle.3 Because it is not yet clear whether there is a real coexistence of two
phases, the term bstateQ will be used instead.4 The splitting of reflections can be observed best for the (113)-reflection,
see Fig. 6.
parameters of the two states differ slightly. One state (this
state will be referred to as state B, because it is the state
that is still present at the end of the experiment)
experiences continuous changes in lattice parameters
during cycling. The a-parameter of this state is monotoni-
cally decreasing (from a=2.8662 at the beginning to
a =2.8202 at a value of x =0.5, see Figs. 7 and 13). The
data was plotted in a way, that shows the x parameter
divided into charge/discharge state. When x reaches 0.5,
the data points are mirrored for clarity reasons (i.e. this
way it can be read as time evolution). The c-parameter
exhibits a monotonic increase from c = 14.202 to
c =14.472 at the x-value 0.5, see Fig. 7. This is exactly
the expected behaviour for this material during cycling.
Fig. 13. Waterfall diagram for the (113)-reflection. For reasons of clarity
only every tenth diffractogram is shown. From bottom to top: start of
experiment (charging), deintercalation until xc0.5, discharging until end
of experiment.
T. Gross et al. / Solid State Ionics 176 (2005) 1193–1199 1199
The other state (state A) shows a different behaviour. It
starts with almost the same cell parameters as the other state
(a =2.8682 and c =14.182 for phase A, see Figs. 7 and 8,
respectively). The a-parameter decreases monotonically
until the value of approximately x =0.75 is reached (the a-
parameter at this point is a =2.8602). From this point
onwards, the a-parameter increases until it reaches
a =2.8692 at the value of x =0.5. After switching from
charge to discharge mode, the a-parameter remains approx-
imately the same. At about x =0.75 (intercalation) the phase
fraction drops below 8% for state A, so at this point it was
decided to use a one-phase structural model. Naturally the c-
parameter should show the inverse effects of the a-
parameter (i.e. when a decreases monotonically, c should
increase monotonically). The expected behaviour is
observed, but only before the polarity is reversed. After
that the c-parameter is increasing (whereas the a-parameter
remains the same) until the phase fraction is too low to rely
on the obtained values (x =0.75 in discharge state).
Fig. 9 shows the phase fraction of state A and B,
respectively. It can be seen that state A transforms into state
B. The irreversible transformation of these states is almost
finished, when the cell is fully charged for the first time
(phase fraction of state A is approximately 15% at x=0.5).
4. Discussion
This study has confirmed the existence of an optimum
temperature range for annealing with respect to cation
disorder and resulting electrochemical performance.
There have been many examinations in the LiNiyCo1-yO2
system, some were done with in-situ methods [19–22], but
most of them were done with EDXD (energy dispersive X-
ray diffraction). It was uncovered that the well known
partial irreversibility of the first cycle could be linked to the
emergence of a new state. The first cycle shows slightly
different trends as the subsequent cycles (which are
reproducible). Ronci et al. [20] already suggested that two
different phenomena occur during the first charging
process5. Because the lattice parameters at the beginning
of the second cycle match the values of the first cycle at
about x =0.9, they suggest that the deintercalation of the first
0.1 equivalents of Li should be an irreversible process. In
this early part of the first cycle a transition of electronic
conductivity occurs [21]. The initial semiconductor behav-
iour is changing to a metallic behaviour. This transition is
the reason why full reintercalation (at normal current rates)
of Li is impossible.
Because of the better resolution of ADXD compared to
EDXD it was possible to separate the two different states of
the material. To our knowledge this is the first structural
5 The second suggestion concerns a process happening at high cell
voltages and deintercalation beyond x =0.25, which is not the case in this
experiment and therefore will not be considered.
examination to prove the irreversible phase transition
occurring during the first cycle for this material.
Acknowledgement
This work was financially supported by the Deutsche
Forschungsgemeinschaft in the frame of project B4 within
Sonderforschungsbereich 595 bElectrical fatigue in func-
tional materialsQ.
References
[1] L. Dyer, B. Borie, J. Smith, G. Smith, J. Am. Chem. Soc. 76 (1954)
1499–1503.
[2] W. Bronger, H. Bade, W. Klemm, Z. Anorg. Allg. Chem. 333 (4–6)
(1964) 188–200.
[3] R.K.B. Gover, R. Kanno, B.J. Mitchell, A. Hirano, Y. Kawamoto,
J. Power Sources 97–98 (2001) 316–320.
[4] I. Saadoune, C. Delmas, J. Solid State Chem. 136 (1998) 8–15.
[5] A. Manthiram, J. Kim, Chem. Mater. 10 (1998) 2895–2909.
[6] R. Alcantara, P. Lavela, J.L. Tirado, E. Zhecheva, R. Stoyanova,
J. Solid State Electrochem. 3 (1999) 121–134.
[7] A. Kinoshita, K. Yanagida, A. Yanai, Y. Kida, A. Funahashi, T.
Nohma, I. Yonezu, J. Power Sources 102 (2001) 283–287.
[8] T. Numata, C. Amemiya, T. Kumeuchi, M. Shirakata, M. Yonezawa,
J. Power Sources 97–98 (2001) 358–360.
[9] G.T. Fey, W. Yo, Y. Chang, J. Power Sources 105 (2002) 82–86.
[10] B.J. Hwang, R. Santhanam, C.H. Chen, J. Power Sources 114 (2003)
244–252.
[11] H. Liu, J. Li, Z. Zhang, Z. Gong, Y. Yang, J. Solid State Electrochem.
7 (2003) 456–462.
[12] C. Delmas, I. Saadoune, Solid State Ionics 53–56 (1992) 370–375.
[13] H. Arai, S. Okada, K. Ohtsuka, M. Ichimura, J. Yamaki, Solid State
Ionics 80 (1995) 261–269.
[14] H. Arai, S. Okada, Y. Sakurai, J. Yamaki, Solid State Ionics 95 (1997)
275–282.
[15] R.K.B. Gover, M. Yonemura, A. Hirano, R. Kanno, Y. Kawamoto, C.
Murphy, B.J. Mitchell, J.W. Richardson Jr., J. Power Sources 81–82
(1999) 535–541.
[16] D. Caurant, N. Baffier, B. Garcia, J.P. Pereira-Ramos, Solid State
Ionics 91 (1996) 45–54.
[17] T. Roisnel, J. Rodriguez-Carvajal, Materials Science Forum, Proceed-
ings of the Seventh European Powder Diffraction Conference
(EPDIC 7), 2000, pp. 118–123.
[18] C. Baehtz, Th. Buhrmester, N.N. Bramnik, K. Nikolowski, H.
Ehrenberg, submitted.
[19] E. Levi, M.D. Levi, G. Salitra, D. Aurbach, R. Oesten, U. Heider, L.
Heider, Solid State Ionics 126 (1999) 97–108.
[20] F. Ronci, B. Scrosati, V. Rossi Albertini, P. Perfetti, J. Phys. Chem.
105 (2001) 754–759.
[21] V. Rossi Albertini, P. Perfetti, F. Ronci, B. Scrosati, Chem. Mater. 13
(2001) 450–455.
[22] V. Rossi Albertini, P. Perfetti, F. Ronci, P. Reale, B. Scrosati, Appl.
Phys. Lett. 79 (2001) 27–29.
[23] J.F. Berar, P. Lelann, J. Appl. Cryst. 24 (1991) 1–5.
[24] J.F. Berar, Acc. in Pow. Diff. II, NIST Spec. Publ. 846 (1992) 63.
